Method of making housing for electrical apparatus



METHOD OF MAKING HOUSING FOR ELECTRICAL APPARATUS Filed Feb. 17, 1949 May 19, 1953 E. slMoN ETAL 4 Sheets-Sheet 2 INVENTORS ELI SIMON FRANK W. THoMAs EDWARD H. BuRKART A geht METHOD OF MAKING HOUSING FOR ELECTRICAL APPARATUS 4 Sheets-Sheet 3 IN VENTORS ELI SIMON FRANKwTHoMAs E. SIMON ETAL.

May 19, 1953 Filed Feb. 17, 1949 EDWARD H. B URKART I Agent May 19, 1953 E. SIMON ErAL METHOD OF MAKING HOUSING FOR ELECTRICAL APPARATUS Filed Feb. 17, 1949 4 Sheets-Sheet 4 DORE LAMINATE GBf---u--LAMINATING RESIN COPOLYM ER BETWEEN' LAMI'NATING R ESI N @fm AND lsooYANATE -ooNTAlNlNG MoLEcuLEs \Q-READT|DN PRODUCT oF ALKYD 25 RESIN-DusocYNANATE Patented May 19, 1953 (cua-agay nes doi Ajoizfller cyanate foam with its inherent high strength characteristics, Thus the method and product of the invention are diiferentiated from the laminated structures of the prior art Where the core material and skin laminations are joined at the interfaces by mechanical locking which is primarily adhesion of the core to the skin lamination by a resin applied to or impregnated in the skin laminae and merely contacting the surfaces of the previously formed and machined core, leaving a distinct interfacial plane or connection of low strength.

A further object of the invention is to provide a method for producing sandwich-type housings and other objects incorporating foamed or cellular plastic cores which utilizes and requiresl only simple and inexpensive equipment. The

only apparatus essential to the method are the male and female mold parts, platens, or the like, andan appropriate oven for the post-curing of the products.

Other objectives and features of the invention will become apparent from the following detailed description of a typical manner of performing the `method in the production of two housings, or the like, throughout which description reference will be had tothe accompanying drawings wherein: Figure 1 is a plan view of the assembled mold employed in vthe method;

vFigure 2 is a vertical sectional view taken substantially as indicated by line 2-2 on Figure 1 illustrating thefemale mold part with the outer skin arranged therein and containing the unreacted mixture for producing the core;

Figure 3 is a view similar to Figure 2 showing the male mold part substantially arranged in place and carrying the other laminated skin;

Figure 4 is a view similar to Figure 3 illustrating the core in the foamed or cellular condition, showing the manner in which the reactant core material holds the skin against the mold surfaces;

Figure 5 is an enlarged fragmentary sectional view taken at line 5-5 on Figure 1 showing the reacting core material rising in the mold cavity between the two skins;

Figure 6 is a vertical sectional view of another female mold part with the skin arranged therein and containingv the unreacted core forming material;

Figure 7 is a View similar to Figure 6 showing the male mold part carrying the inner skin laminations and being arranged in place;

Figure 8 is a view similar to Figure 7 showing the male mold part in the nal position and illustrating the core material in the foamed or cellular state where it holds the skin against the mold surfaces; Figure 9 is an enlarged fragmentary perspective View of the housing or product made in accordance with the method as illustrated in Figures 6, 7 and 8;

Figure 10 is an enlarged fragmentary sectional view illustrating the several laminations of one of the skins of the product; and

Figure 11 is a diagrammatic view on a greatly enlarged scale illustrating the skin and interfacial area of the product and showing the interspersion of the cellular core material and laminating resin.

The method provided by this invention is useful in making objects and devices varying greatly in intended use or application. For example, the devices may be simple panels, sheets, or cov- .transmitting and/or receiving equipment, it being understood that this is only one typical application of the invention.

The method of the invention, as illustrated in Figures 1 to 5 inclusive, may be said to comprehend the `general'steps of providing outer laminating material or skin material I4 on the sur faces of a mold I--I2, introducing a reactant alkyd resin-polyisocyanate mixture I5 into the skin-lined mold cavity, allowing the mixture `to react to form a foamed or cellular core I6 between and bonded with` the skin laminations I4, and then preferably post-curing the resultant laminated structure at slightly elevated temperature.

In Figures 1 to 5 inclusive, the mold includes a female part lil having a central cavity II and a male part I2 adapted to conform generally to the cavity. The upper end of the mold cavity I I remains open to atmosphere at all times while the lower end of the cavity is closed and, in the particular case illustrated, is spherically concave, it being apparent that the cavity may have practically any required configuration. 'I'he male mold part I2 may be a recessed or hollow member to be of reduced weight and in the typical case illustrated is shaped so that its external surface is substantially parallel with and equally spaced from the wall of the cavity II when the mold parts are in their final positions. The part I2 is adapted to extend upwardly beyond the upper surface of the part Il) and its projecting portion has spaced radially projecting ears or lugs I3. These lugs I3 are adapted to rest on the upper end of the mold part II) to support the part I2 and, if desired or necessary, spacers may be associated with the lugs to obtain the desired spacing between the walls 0f the cavity II and the surface of the male mold part I2. Furthermore, if desired, studs, clamps, or the like, may be used to secure the lugs I3 to the moldpart IU and thus maintain the desired relative positions of the mold parts, although suchA details are not essential to the method of the invention.

The initial steps of the method, as practiced in accordance with Figures 1 to 5 inclusive, are the provision of the outer or skin materials I4 and the lining of the mold surfaces with these materials. The materials I4 used for this purpose will, of course, depend to a considerable extent upon the intended use of the product being manufactured. Where the product or housing is designed for the transmission of radar or microwave energy, the skin materials or laminations I4 may be fibre glass fabric, superimposed layers of non-impregnated or non-bonded bre glass cloth, felt, fibre glass matting, or other materials that are substantially transparent to radar energy. While, in most cases it is preferred to employ a plurality of superimposed layers of such material I4 on the surfaces of the cavity II and mold part I2, Figures 1 to 5 illustrate, for the sake of clarity only one layer or thickness of the fabric I4 of the class above named on each mold surface. Figure 10 illustrates on a much larger scale a portion of a housing having a plurality of description of both mannemof'carryingioutwthe method of: the invention. where wefemploy.' the expressions` skin` fabric I 4j skin material I 4; or Athe, equivalent; we refer to multi-layer skins aS shown inAFigure 10 asv/ellas; the single layer` sk ixn The skin-materials I4 are arrangexltocom-v plellely. coverv the walls Of the.. Cavity lli and .the surface of;tl'1e mold-partflZ `at least tothe height r level, where theihousins is: to beL trimmed oil or.1 finished; In this? manner vof performing the methodithekii materials; I I: mayweither-be prefamiedf and: prelaminated, that. is. impregnated with a laminating resin and then formed; or shaped-to t theirrespective vmoldssurrces-,- the being cured so, that. the. Y skin materials are sul weianfiall-yI rigidy and selffsuppcrtina. or the materiels I 4 may -be unlaminated-,andwvithe out resin either: cli-reg or -uncured-in, which case appropriate-.Care isftaken Vtofarrarlse anfisupport the-softimforntedskin materials I4 on their re. spective .moldsurfaces Where the skin materials. Lkhave @plurality of Y layers it is -preferreflfto otfset the edgesoi adjacent layers-so that suhstantiallyvuniform strength is obtained.

The next `operation is theintroduction into the lined moldgcavity: I-i of a lsuitable.quantityoi a cellular'Y plastic.y producingk material: or mixture: I5E `Figui-1e 2 illustrates a body of the liquidlreactant mixture I5 in thelcwer portion of the cavity II, lined by the skin material i4. It isfpreieredto employ a reactant allfycl resinmeta-toluenel diisocyanate mixture of thevclass ydescribed and claimed in the copencling applicationof Eli Simon land Frank W. Thomas, Serial Ncl y 77,058, filed.February'17I 1949, now Patent Nq 2,591,884..grantedApril8, 1952. The following are typical formulae of this caseofV reactant cellular plastic producing compounds:

Formula 1 Grains Anialkydresinhaving an acid number 01"20- anda water contentof 0.85% `by-weight obtainedfromfthereaction of 4 Lmols tri-Y. methylol propane, 2.5'mols adipic acidand Alkyd resin .of Formula ,1 having an .acid number of and a water` content ,of 0.85% by weight Meta-toluene diisocyanate, containing 2 grams of ethyl cellulose having a viscosity of l100 centipo'ises and an ethoxyl content of from4i8.0 to 49.5 %'per 100 grams ofthe meta-toluene diisocyanate g 20 Zinc stearate powder ll/ Dlallylphenyl'phosphonate 5 Benzoyl peroxide 0.25

In Formularen, 2 :and and'lin similarxiormulas. tions 1the-.concentrationsrangerof theiethylicelluilose additive is from0.0,3 gram-.- to; 15p-grams; for each gramsV of the .meta-toluene-.diisocyanate: The ethyl. cellulose; employed-,in such formula: tions mayfhave an Yethoxyl zcontent rangeiorom 45.0;fto- 49:5 and a: viscosityn of; 7 Vcentipcisessto approximately; 2.00fcentipoises withafpreferable viscosity of approximately 5,0.'to, lc'centipoises. The reactant, mixtures; off these; and similar formulations; react at'. atmospheric: pressure-f to greatly increasetheirixvolumes and to produce high strength; lightweight .cellular plastics;hay` ing very small uniform cells. The cellular plastics thus.` obtained have high. compressive strengthilhgh tensile,strength,k and good shock and Vibration resistance' characteristics,... Eure thermore, it has been found-.that suc-liA cellular plasticsrvare highly transparent. to radar energy producing 5a, minimurrroi` attentuation losses.y In fact, ithas been found :that all ofthe alkyl resi-11? diisocyanate cellular` plastics.4 of theclasses. herein described are. effectivey in the transmission of such l energy except Athose :incorporating .metallic leang powders. Whereit is required that .the latter types of foarned` plastics transmit radar energythe formulations may be readily changed by.merely substituting. anyof thefmetallic soap powders. hereinafterset forth for the metallic. leaiing powder component. The. following formulae are typical. of those. incorporating metallic soap. powders... and metallic leaing powders:

Formula x 4 Grams Alkyd resin of Formula 1 30 l'lolyisocyanato reagent containing; meta--- toluene diisocyanate; and 0.065 moll-.0h21l methyl, 2-4 pentanediol for. each-mol of.

meta-toluene diisocsttnate 20 Zinc stearate powder 1.12 Dallyl phenyl phosphonate 5 Benzoyl peroxide.; 1/4.

Formula `5.'

, Grams Alkyd resin of :Formula .l` v30 P olyisocyanate. reagent.' containing. meta.-

toluene `diisocyanate and from 1-0-01 to 025i mol of toluene diamine vforeach vmol of;the metaztoluenediisocyanate 20 Aluminum leaiing.A powder 2 The reactant mixtures of Forniulae 4 and 5 are..

of the class describedand claimedjin the copend. ingl application of. Eli Simon and' Frank W." Thomas; Serial No. 71,037, filed January 14, 1949; now nPatent No. 2,602l783.

Following thev introduction of v* the reactant plastic 'material I'5 into Ythe lined'fernale Arn'olcl I Il; the male 'mold `part "I 2icarrying its skin-material I4, is yentered inthe cavity- 4I i and properly posi; tioned with respect to the mold" partfIU Figeure\3 of thedrawings shows `the' mold'part" I2 beingentered into the' cavity-| I: Iti-Will-be ob served Ythat the reactant fliquidfalkyd- #resin-poly-i isocyanatemixtureV I 5* is Ppartially displaced uprward bythe mold parti-2 and'that the upper'end of the 4mold cavity remains open ltothe atmos-i phere. A suicient quantity-of thereactant mix-i ture --I'5 is provided in the Amold to assure'a full or adequate J-lling of the space -Abetweenthe v lined walls of they cavity I! and fthe-covered'or lined part I21bythe cellular plastic.V In practicethe allsydI resin-polyisocyanate Vmixture vreacts at 'atmospheric ypressure i to produce a' multitude of small; generally"uniforrn` spherical Vgas filled cells 7 throughout the entire core I6 and the foamed or cellular plastic mass 'or core I 6 may rise in the mold space, as shown in Figure 5, to spill over the top of the mold assembly in the manner illustrated in Figure 4. While not essential, it is preferred to maintain the mold parts at a temperature of' about 120 F. during the reaction of the core forming cellular material. The foam producing reaction of the material I is accompanied by the exotherrnic heat and pressure, the heat assisting in curing the resin and the presn sure serving to urge the skins I 1i firmly and evenly against the Walls of the mold. Where the skin material Ill has been prelaminated and preformed, the cellular plastic It adheres to and bonds with the inner surfaces of the laminated material Ifl. The resin employed in the prelaminated skin material lll is preferably compatible with the alkyl resin-polyisocyanate reactant mixture but the latter securely bonds with and adheres to practically all skin materials and the laminating resins employed therein and, in fact, strongly adheres to most materials. Where the skin materials I4 are prelaminated and preformed and contain polymerized cured resins or plastic, the material of the cellular plastic core i6 will not penetrate the skin materials I4 to any appreciable extent and will not engage the walls of the cavity il or the surface of the mold part I2. Therefore, upon completion of the reaction of the core it and following ythe initial setting and curing of the core material,

the product or housing may be removed from the mold following Withdrawal of the male mold part I2. The product or housing is then preferably post-cured at a temperature of from 125 F. to 225 F. for from l0 to 12 hours to continue polymerization of the reaction and thus obtain a stronger more heat stable core IB.

When the skin materials ill are not prelami nated and not preformed but are in the nature of one or more layers of dry, porous, or soft fabric, felt or the like, the reactant alkyd resin-polyisocyanate liquid or plastic material I5 penetrates the skin materials Iii and therefore will reach the wall of the cavity Il and the surface of the mold part I2. Accordingly, it is desirable in this case to. coat or cover the surfaces of the mold with a parting material prior to arranging or positioning skin materials Ill in the mold so that the alkyd resin-polyisocyanate mixture will not adhere to the mold wall. Graphite, deposited from oil-dag, water-dag or alcohol-dag, or mineral oil, or the like, may be used as the parting material. Where the article being produced is to be used with radar equipment, it is preferred to-use mineral oil, or the like, as a parting material. The penetration of the skin materials Ill by the reactant alkyd resin-polyisocyanate mixture I5 results in a particularly effective lamination or bonding of the several layers of the skins It and a strong uniform andv continuous bonding or merger of the skins I4 with the cellular core I6. The material I5 that enters the skin it and that occupies the zones at the inner faces of the skins I4 reacts in the same manner as the material in the main mass of the core Iii to produce a cellular, high strength, low density plastic characterized by extremely small pores or cells of uniform size and shape. The foamed or cellular plastic coats embeds and bonds with the layers, strands, threads and libres of the skin material I@ so that the skins are, in effect, cast or embedded in the self-same material that constitutes the core I6 with no plane or zone of contrasting or differing physical characteristics existing at the interfaces or planes of joinder of the core `lli and skins I4. This results in a product or structure of great strength, uniform composition and uniform physical characteristics and of uniform described.

The housings or devices produced, as above described, each comprise a continuous one-piece core I 6 of foamed or cellular plastic and internal and external skins I of fibre glass fabric, felt, or the like, laminated and impregnated with resin or plastic. The sandwich-type construction, or laminated construction, is exceedingly strong and yet has a very low density owing to the low density cellular plastic core it. VThe products have good dielectric characteristics, and, as above pointed out, pass or conduct microwave energy, etc. with but slight loss. The products may be cut or machined as found necessary and it is usually preferred, or at least desirable, to trim off the rough or uneven upper or open ends of the housings to bring the housings to the desired size vand shape.

The method of the invention, as illustrated in Figures 6 to 9 and 1l, comprises, generally, substantially the same steps or operations as above described, except thatthe skin materials I4 are wet or saturated with a laminating resin prior to or upon being arranged on the surfaces of the mold 2li-22.

The female mold part 20 has a recess 2l ofthe selected or required configuration and the male mold part 22 is shaped to conform to the recess and leave a mold space or cavity of the required thickness and shape. This mold cavity is at all times open at its upper end to the atmosphere and the male mold part 22 may be supported in the correct position on the part by lugs 23 engaging the top surface of the part 2U. In this particular mold arrangement it may be assumed that the parts 2li and 22 are elongate and that the housings or objects to be formed therein are elongate chambered or hollow members having somewhat curved side walls converging to a rather abrupt or sharp edge, although it is to be understood that the mold may be designed to produce objects of practically any shape.

The skin material Ill may be of the same nature as above described, that is, Ait may be one or more layers or plies of fibre glass fabric, -bre glass matting, felt, or the like, or combinations of such materials. However, in this manner or process of carrying out the invention the skin materials I4 are saturated or partially saturated with what we term a laminating resin prior to or at the time they are arranged on the surfaces of the mold 2li-22 and the alkyd resin-diiso cyanate reactant mixture I5 is allowed or caused to react in the mold space dened by the wet skin material I4 so that the foaming alkyd resindiisocyanate product copolymerizes with the laminating resin to produce or provide'in the product diffusion zones of cured or hardened resins. These diffusion zones, which are coextensive with the marginal portions of the core I6, as well as with some or all of the laminated or single ply skins I4, are areas tions graduate or change gradually from sub- Whose composi-A stantially pure laminating resin to the substantially pure alkyd resin-diisocyanate reaction product of the core. One of these diffusion interfacial zones is illustrated diagrammatically, on an enlarged scale, in Figure 11, as will be more-fully described below. To facilitate a fuller understanding of the copolymerizing action obtained when the material of the core i6 reacts in the mold space between the skins I4 which carry or are saturated with the laminating resin, we will describe several alkyd resin-diisocyanate reactant mixtures and several suitable laminating resins and the mechanism of the copolymerization of the same at the interfacial diffusion zones of the housing or product.

The alkyd resins which we preferably employ in the polyisocyanate reactant mixtures are the reaction products of polyhydric alcohols and polybasic acids unmodied or modied with oil and/or other resins and having an acid number of from to 80, a water content of from 0.1% to approximately 3.0% by weight and having the following ratio range of the hydroxyl. to the carboxyl groups in the alkyd resin reactants:

From a'hydroxyi (on) :1 earboxy1 (COOH) To 4 hydroxyl (OH) :5 carboxyl (COOH).

It is usually preferred to employ alkyd resins having an acid number of between and 25 and wherein the ratio of the hydroxyl groups to the carboxyl groups is 2 to 1. The following formulae are suitable for preparingl unmodified alkyd resins from polyhydric alcohols and polybasic acids, the ratios of the hydroxyl groups to the carboxyl groups in the alkyd resin reactants of these formulae being 2 to 1.

Formula A' Mols Glycerol 4 Adipic acid 2.5 Phthalic anhydride 0.5

Formula B Mols Glycerol 2 1,4 butylene glycol 1 Adipic acid 2 Formula C Mols Trimethylol propane 4 Adipic acid 2.5 Phthalic anhydride 0.5

In Formula A from 3 to 5 mols of glycerol, from 1.5 to 3 mols adipic acid and from 0.1 to 1.51mols of phthalic'anhydride may be used while Virl-Formula C the practical operative range of proportions is from 3 to 5 mols trimethylol propane, from 1.5 to 3 mols adipic acid and from 0.1 to 1.5 mols phthalic anhydride. The following Formulae D and E are suitable for preparing unmodified alkyd resins from single polyhydric alcohols and single polybasic acids productive of resins suitable for use in the cellular plastic mixture.

Formula D Mols Glycerol 4 Adipic acid 3 Formula E Mols Trimethylol propane 3 Phthalic anhydride 2 The ratio of the hydroxyl groups to the carboxyl groups in the alkyd resin reactants of Formula i meta-toluene diisocyanate.

D is 2(OH) :1(COOH) and in Formula E this ratio is 9(OH) :4(COOH). The following Formula F is an example of an oil mcdied alkyd resin suitable for employment in the reactant cellular plastic producing mixture, the ratio of the hydroxyl groups to the carboxyl groups in the alkyd resin reactant being 3(0H) :31/2 COOH).

Formula F Mols Glycerol 1 Phthalic anhydride 1.5 Oleic acid 0.5

The following Formula G is an example of a natural resin modiiied alkyd resin suitable for incorporation in the cellular foamed plastic core material, the ratio of the lhydroxyl to the carboxyl groups being 1 to 1.

Formula G Glycerol gram mol l Sebacic acid do 11/ Resin copal grams We have found that the most satisfactory results are obtained when the water content range of the alkyd resin component of the diisocyanate alkyd resin reactant mixture is from 0.1% to 3.0% by weight without regard to the specic manner of incorporating the water in the mixture. In the typical examples herein set forth, it will be considered that the water component of the diisocyanate-alkyd resin reactant mixture is incorporated by dissolving a calculated amount of the water in the selected alkyd resin and suitably agitating the resin-water mixture so that the alkyd resin component will contain the selected proportion of water. However, as set forth in the copending application of Eli Simon and Frank W. Thomas, Serial No. 35,294, filed June 25, 1948, now PatentNo. 2,577,279, the water may be incorporated in the reactant mixture in combination with a non-ionic wetting agent or by the use of one or more salt hydrates.

The isocyanate employed in the alkyd resin polyisocyanate reactant mixture is preferably As described and claimed in the copending application of lEli Simon and Frank W. Thomas, Serial No. 50,007, led September 18, 1948, now Patent No. `2,577,728, metallic soap powders may be incorporated in the diisocyanate alkyd resin reactant mixture to serve as lfoamingagent stabilizers and thusobtain superior results. The metallic soap powders that are eiiective for this purpose are metallic soap powders of fatty acids having from 12 to 20 carbon atoms including: l

@Zinc stearate Aluminum stearate Calcium stearate Magnesium stearate Magnesium hydroxy stearate Barium stearate Zinc laurate Calcium oleate strontium stearate molecular weight thermoplastic nlm producingl polymeric resin additives which serve as nlm stabillzers.

cells and having superior physical strength. Furthermore, the additives permit the use of a higher Water content in the alkyd resin-metatoluene diisocyanate system, for example a water content of by weight, thus reducing the density of the cellular plastic material. Further. it has been found to be p-articularly advantageous to employ the high molecular weight polymeric additives in the cellular plastic material of the cores Where the product or yarticles of this invention are to be used in association with radar equipment.

The high molecular weight polymeric resin additives are lsoluble in the meta-toluene diisocyanate and may or may not react therewith. Included among these additives that are productive of a more effective small cell roamed plastic core material are:

1. Ethyl cellulose-' This polymeric resin has a molecular weight of approximately 130,000 and it is preferred to employ an ethyl cellulose having from 43% to 50% ethoxyl content. The best results have been obtained where the ethoxyl content is from 45% to 49.5% and where the viscosity is between 50 and 100 centipoises.

2. Polymeric chlorinated natural rubber- This product has an average chlorine content of 67% and a 'preferred viscosity of lbetween 125 and 1,000 centipoises l 3. Polymeric acrylate and methacrylate resins and their cli-polymers (prepared by polymeriz'ing lower esters of acrylic and methacrylic acid):

a. Methyl methacrylate b. Propylmethacrylate c. Isobutyl methacryla'te d. Butyl methacrylate e. (Jo-polymer of methyl acrylate and ethyl methacrylate.

4. Benzyl celluloseformed by the reaction of benzyl chloride with alkali cellulose.

. Polystyrene.

. Polydichlorostyrene.

. Natural rubber (polymeric isoprenel the ymolecular weight of natural rubber has been variously determined as ranging between 100,000 and 300,000.

8. Polyvinyl butyral.

.9. Polymeric vinyl chloride-vinyl acetate copolymers:

a. Containing approximately 87% vinyl chloride and 18% vinyl acetate `and having a. molecular weight ot approximately 6,000 to approximately 25,000V

b. Containing from 00%. to: 95% vinyl chloride.

Polyvinyl acetate tproduced by polymerization of vinyl acetate). The molecular weights of thepolyvinyl acetate `suitable for incorporation in the cellular plastic formulation range from approximately 10,000 toi approxi:-

mately 50,000.

Polyvinyl. chloride (having au average molecular yweight of approximately 5,000).

The concentration or proportion oi the selected high molecular weight polymeric resin emplayed may be varied considerably. For example These additives result in the product' tion of foamed plastics having very small uniform from 0.03 gram to 15 grams of the ethyl cellulose or from 5 to 20 grams of the chlorinated natural rubber may be used with each 100 grams of the meta-toluene diisocyanate as incorporated :in the reactant cellular foamed producing mixture.

The cellular plastic `core materialemployed-in the method and product of the invention may be made ame resistant and self-extinguishing when once ignited by incorporating flame retardant additives in the alkyd resin-meta-toluene diisocyanate reactant mixture. Such additives are unsaturated alkyl esters of aryl phosphonic acids namely compounds having the general formula: ArPO(OCH2CR:CI-IR1)2 where Ar .represents aryl and alkaryl hydrocarbon radicals and R and R1 are hydrogen and alkyl hydrocarbon radicals. Compounds of this character are described in United States Letters Patent No. 2,425,765 issued August 19, 1947, `and include:

1. Diallyl phenyl phosphonate 2. .Bis (methallyl) benzene phosphonate 3. Diallyl toluene phosphonate These additives, in addition to imparting name resistance and to decreasing flame propagation characteristics of the roamed cellular product, als-o serve to materially decrease the density of the roamed material. In practice, from 1 gram to 20 grams of the flame resistant additive may be employed with each 30 grains of the alkyd resin. Where such nre resistant additives are employed it may be found desirable to predissolvc benzoyl peroxide in the additive in the propor-l tion of approximately 5% by weight of the additive. The following are typical examples of the alkyd resin-meta-toluene diisocyanate reactant formulations for the core forming mixture 15:

Example Y Alkyd resin of Formula C having an acid number of 20 and a Water content of 0.85% by weight 60 Meta-toluene diisocyanate containing 2 grams of ethyl cellulose, having a centipoise viscosity of 7 and an ethoxyl con tent of from 46.8 to 48.5 per 100 grams of meta-toluene diisocyanate 40 Diallyl phenyl phosphonate 10 Benzoyl peroxide 0.5

Example II Grams Alkyd' resin of Formula C having an acid number of 20 and a water content of 0.85%- by weight Meta-toluene diisocyanate containing 1 gram of ethyl cellulose, having a centipoise viscosity of 200 and an ethoxyl content of from 46.8- to l48.5 per grams of the meta-toluene diisocyanate 40 Diallyl phenyl phosphonate I0 Benzoyl peroxide 0.5

Example III Grams Alkyd resin of Formula C having an acid number of 20 vand a Water content of Grams Earample IV Grams Alkyd resin of Formula C having an acid number of 20 and a water content of 0.85% by weight 60 Meta-toluene diisocyanate containing 2 grams of ethyl-cellulose of 100 centipoise viscosity and an ethoxyl content of 48.0

to 49.5% per 100 grams of meta-toluene diisocyanate 40 Example V Grams Alkyd resin of Formula A having an acid number of 16 and a water c ontent of 0.87% by weight 30 Meta-toluene diisocyanate 20 Zinc stearate powder 2 Diallyl phenyl phosphonate Benzoyl peroxide 0.25

Example VI Grams Alkyd resin of Formula C having an acid number of and a Water content of 0.85% by weight Meta-toluene diisocyanate containing 5 grams of chlorinated natural rubber of 1,000 centipoise viscosity per 100 grams of the meta-toluene diisocyanate 20 Diallyl phenyl phosphonate 5 Benzoyl peroxide 0.25

Example VII Grams Alkyd resin of Formula C having an acid number of 20 and a water content of 0.85% by weight 30 Meta-toluene diisocyanate containing 4 grams of benzyl cellulose per 100 grams Furthermore, the reactant core-forming mixture I5 may be of the character employed in the previously described form of the invention and of the kind set forth in Formulae 1 to 5 inclusive. When the article being produced is required to transmit radar energy it is not desirable or in the formulations. e

'I'he above mentioned laminating resins appliedv to or impregnated in the skin materials I4 may be thermosetting plastic resins or blends or mixtures of thermosetting resins and thermoplastic resins. The laminating resins of the skin materials I4 are capable of copolymerizing With the foaming alkyd resin-diisocyanate reaction products to result in diffusion zones of cured or hardened resins, which zones are characterized by a gradual gradation in content from substantially pure laminating resin in the outer portions or laminae of the skins I4, to intermediate areas at the interfaces of the core I6 and skins I4 containing laminating resin molecules, alkyd resin-diisocyanate reaction product molecules and molecules of the =copolymer between the laminating resin and the reaction product and thence to the substantially pure alkyd resin-diisocyanate reaction products of the core IE. The nature of these diffusion zones, as we believe them to be constituted, is illustrated in Figure 11 which diagrammatically represents on a large scale a small area of a skin I4 and adjacent portion of the core I6 in cross section. In Figure 11, as indicated by the legends, the material of the core I6, that is the reaction products of alkyd resin-diisocyanate mixture are represented by the circles 25, the laminating resin molecules are represented rby the circles 25 enclosing the crosses, while the co-polymer between the laminating resin and the isocyanate containing molecules are represented by the circles 2'I enclosing the diagonal lines. It will be seen from an inspection of Figure 1l that the interfacial area, Where the mass of the core I6 joins the innermost skin layer I4, has substantially equal numbers of the three above named molecules 25, 25 and 2'I, while there is little or no penetration of the substantially pure core material molecules 25 into the skin I4 there are a considerable number of the (zo-polymermolecules 21 between the innermost skin layer I4 and the adjacent lamination I4. The number of these molecules of the co-polymer gradually lessen in the succeeding laminations I4 until there may be none in the outermost skin lamination. The ldiffusion area or zones of graduated or merging physical composition and physical characteristics assure great strength inthe laminated or sandwich-type product resulting in a product much superior to the typical laminated structures where there are distinct planes or limited sectional areas of abrupt change from one material to the other. j .Y

The laminating resins capable of copolymerizing with the reaction products of the alkyd resin and diisocyanate of the core Itl may be selected from substantially different classes of resins or compounds including: Y

(a) Unsaturated polyesters containing more than one Vinyl group per molecule so as to be capable of cross linking and forming insoluble thermosetting type resins. Included in this classification are the reaction products of maleic anhydride with a glycol such as di-ethylene glycol which, after the initial reaction are further heated, and condensed to yield the linear polyester:

HOOC- H (2) Bis(.methallyl) benzene phosphonate oHl=o-oiiio-1l-ocn2-o=oai i CH3. CH3

(3) Dallyl toluene phosphonate (o) Unsaturate'd alkyl esters of alkenyl phos-` plionie acids of the general class disclosed in the United States Letters Patent No. 2,425,766 issued August i9, 1.947:

(l) Diallyl isobutene phosphonate cao-ona E o H3 (2) Diallyl styrene phosphonate Hilfs@ (3) Bis (methallyl) styrene phosphcnate $33 (IHs CHzriO-C'HnO--P-O @Hr-3:0132

site@ (d) Diallyl phthalate (e) Allyl, methallyl or crotyl glycol carbonates, suoli as bi's.(a'l1yl) dietl'lylene glycol carbonate:

If desired, the laminating resin may comprise a blend ormixture of a selectedunsaturated poly- I6 compound which serves as a copolymerizlng additive. For example, the unsaturated polyester between diethylene glycol and maleic anhydride with the polymerization carried to an acid number of from l0 to l0 may be mixed with any of the following thermoplastic monomeric vinyl compounds, each having one vinyl group per molecule to constitute the laminating resin.

(a) S'tyrene (vinyl benzene) (b) Dichloro styrene H C=H1A (c) Acrylonitrile (vinyl cyanide) H' H Ho=ocN (d) Vinyl acetate H o1 HCL-:l-Cl

(f) Vinyl chloride (g) Diphenyl ethylene (h) Methyl vinyl ketone Ciego-C4111;

H Il

(i) Methyl methacrylate y n Capocaccia as (j) Vinyl esters, such .as ethyl vinyl ether HHC:`

oozH

Where the laminating resin for the skin .material I4 is a mixture of the unsaturated polyester and lthe monomeric mono-Vinyl compound, there may be from 10 to 100 parts 'by weight of the monomeric compound for each 1'00 parts vby Weight of the unsaturated polyester resin.

The present invention, as illustrated inFigures 6 to 11 inclusive, being directed to the method of making laminated products is not ,directly .concerned with the theory of the ychemical action or mechanism attending the copolymerzing of the isocyanate 'containing molecules of the foaming core material l5 with the laminating resin. However, it appears that there are two ways in which this copolymerization takes place:

(1) By the reaction of the isocyanate containing molecules of the material comprising the core ester, Such aS abOVe named, and a mOIlOmGlC 15 |'6 withthe hydroxyl (OH) and/or With the car- `amiante 17 v18 boxyl (COOH) groups of the laminated resin. spherical cells of the internal areas of the core Thus: I6, leaving a weak interfacial zone. However,

H O C-C H (linear polyester of diethylene glycol and maleic anhydride) where R=structure attached to an isocyonate when the skin laminating resin is uncured at the group time the core material I5 is reacted in the mold,

HO O C-CH H H H HC--J-C O (CHDzC (GB01- O C=C-C O CHDQO (GEMM-(I) H C-N-R Il O (additional reaction with terminal (OH) group resulting in formulation of a urethane) (reaction with terminal (COOH) group resulting in amide structure and liberating carbon dioxide) (2) By the addition copolymerization of the this elongation of the outermost cells of the core activated isocyanate groups of the core material I6 is eliminated or at least reduced and because I5 with the activated vinyl groups of the laminatthe above described interfacial zone contains the ing resin Thus; co-polymer of the core material and the laminat- R-N--C-O -l- Peroxide-type catalyst (benzoyl peroxide) -I- heat diallyl phenyl phosphonate It is to be understood that in the invention as ing resin, the interfacial zone is materially practiced in Fgures to 11 inclusive, the lamistrengthened instead of being weakened.

nating resin on, or incorporated in, the skin 5y The reaction of the alkyd resin-isocyanate material I4 is unpolymerized and in a liquid or mixture I5 is also accompanied by heat and this semi-liquid state when the reactant core producexothermic heat cures` or polymerizes the lamiing material or mixture I5 is introduced into the nating resin. Thus the laminating resin is polymold cavity and allowed to react. The reaction merized and initially cured simultaneously with 0f the material I5 is accompanied by the de- 5j,y the core I6, making for a more uniform and velopment of gas pressure which urges the skin stronger product. As in the previously described materials I4 outwardly into conforming engageform of the invention the mold 20-22 may be ment with the walls of the mold and which brings maintained at a temperature of about 120 F. the reactant foaming isocyanate containing mixduring the foaming reaction.

ture I5 into direct and intimate contact with Gf) Following the pouring and reacting of the core the laminating resin so as to admix therewith. i6 the product iS preferably gVeIl a DOSt-Cule at This admixing of the foaming isocyanate confrom 125 F. to 225 F. for from 10 to 20 hours.

taining mixture l5 with the laminating resin is The finished product may be machined as reimportant in that it not only brings about the quired and it is usually preferred t0 Cut 0r trim above described copolymerization of the two ma- Off the uneven upper Portion Where Jthe Gore materials but also because it reduces the friction terial has spilled over the '60D 0f the mOld.

between the rising foaming mixture I5 vand the Laminated products or articles such as manuskins I4. When the foaming core material I5 factured in accordance with the methods herein rises along the surface of a dry precured lamidescribed form the Subject 0f 0111' @Opendirlg apnated skin the marginal cells of the core I6 are 7p DlCaliOn Serial Number 183,384 filed OCOber 4, found to be elongated in the vertical direction 1950.

due to the friction or resistance to Vertical mo- It should be understood that the invention is tion offered by the pre-cured skin. The resultant not based upon 0r dependent upon the theories elongated cells of the core I6 are somewhatwhich we have expressed. Nor is the invention weaker than the uniform and substantially to be regarded as limited to the express procedure -or materials set forth,=these details being given ing a wet polymerizable unsaturated organic substance containing at least two groups per mole cule as the reactive constituents, said groups being selected from the class consisting of vinyl groups and allyl groups, said substance being,

capable of Iccpolymerizing with isocyanate molecules, and then bonding a cellular plastic layer with said material by contacting a reactant cellular plastic isocyanate-containing mixture with the wet organic substance-carrying material, and

a mold, and then forming a cellular plastic layer between and bonded with the skin laminations by introducing into the space between the skin laminations a reactant isocyanate-containing resinous mixture while said polymerizable material remains wet, and allowing the mixture to react to form a cellular plastic layer, to copolymerize with said material in the interfacial zones of the layer and laminations, and to cure said material in the laminations,

5. The method of making a laminated article comprising impregnating fabric skin lamnations with a wet polymerizable material comprising an unsaturated polyester which is the reaction product of a dihydric alcohol and an alpha unsaturated, alpha-beta dicarboxylic acid; and a monomeric compatible co-reactive compound containing groups selected from the class con#- sisting of vinyl groups and allyl groups, said polymerizable material being capable of copolymerizing with isocyanate-containing compounds,

` arranging the vwetskin laminations inspaced then allowing the mixture to react to form the cellular plastic layer and to copolymerize with said organic substance of said laminating material.

. 2. The method of making a laminated article comprising impregnating skin material with a wet polymerizable unsaturated organic material containing lat least two groups per molecule as the reactive constituents, said groups being selected from the class consisting of vinyl groups and allyl groups, said material being capable of copolymerizing with isocyanate-containing compounds, supporting the impregnated Iskin material, and then providing a layer of cellular plastic material bonded to the skin material by contacting the wet impregnated skin material with a reactant isocyanate-containing resin mixture, and allowing said mixture to react to form a cellular plastic body while said polymerizable material and mixture copolymerize to constitute a diffusion zone between said skin and body containing molecules of said polymerizable material and said mixture.

3. The method of making a laminated article comprising impregna'ting fabric skin laminations with a wet polymerizable unsaturated organic material containing at least two groups per molecule as the reactive constituents, said groups being selected from the classV consisting of vinyl groups and allyl groups, said material being capa* ble of copolymerizing with isocyanate-containing compounds, arranging the skin laminations in spaced apart relation and then providing a cellular plastic layer between the skin laminations and at the same time curing said polymerizable material by introducing into the space between the skin laminations a reactant isocyanate-containing resin mixture while said resin remains wet, and then allowing the mixture to react to form the cellularlayer, to copolymerize with said material in a diffusion zone between said layer and the skin laminations, and to cure said in the laminations.

4. The method of making a laminated article comprising impregna'ting skin laminations with a wet polymerizable unsaturated organic material containing at least two groups per molecule as the reactive constituents, said groups being selected from the class consisting of vinyl groups and allyl groups, said material being capable of copolymerizing with isocyanate-containing compounds, arranging the skin laminations in spaced apart relation by placingthe'm on the walls. @.f

apart relation by engaging them on the Walls of arnold, and then forming a cellular plastic core between and bonded with said laminations while simultaneously curing said polymerizable material by introducing a reactant alkyl resin-diisocyanate mixture into the space between said laminations while said polymerizable material remains wet, and then allowing the mixture to react to form the core, to copolymerize with said polymerizable material at 'the interfaces between the core and laminations, and to cure the polymerizable material in the laminations.

. 6, The method of making a laminated article comprising impregnating inorganic fabric skin laminations with a wet polymerizable material comprising an unsaturated polyester which is the reaction product of a dhydric alcohol and an alpha unsaturated, alpha-beta dicarboxylic acid; and a monomeric compatible co-reactive compound containing groups selected from the class consisting of vinyl groups and allyl groups, said polymerizable material being capable of copolymerizing with isocyanate-containing compounds, arranging the skin laminations in spaced apart relation by engaging them on the walls of a mold, forming a cellular plastic core between and bonded with said laminations while simultaneously curing said polymerizable material by introducing a reactant alkyd resin-diisocyanate mixture into 'the space between said laminations while said polymerisable material remains wet, allowing the mixture to react to form the core, to copolymerize with said said polymeriaable material at the interfaces between the core and laminations, and to cure said polymerizable material in the laminations, and then post-curing the article at from F. to 225 F. for from l0 to 20 hours.

'1. The method of making a laminated article which comprises providing a porous fabric skin, inripregnatingl the skin with. a liquid polymerizable material comprising an unsaturated polyester which is the reaction product of a dihydric alcohol and an alpha unsaturated alpha-beta dicarboxylic acid, and a monomeric-compatible coreactive compound containing groups selected from 'the class consisting of vinyl groups and allyl groups, and then bonding a body of cellular plastic with the skin by contacting a mass of a reactant isocyanate-containing resinous mixture with the skin while said polymerizable material remains wet, and allowing said mixture to react 'to form the cellular plastic body, to copolymerize 21 with said polymerizable material in the interfacial zone between said skin and body and to cure the polymerizable material in the skin.

8. The method of making a laminated article which comprises providing a porous-material skin, impregnating the material of the skin with a liquid unsaturated polyester containing two or more vinyl groups per molecule, and then bonding a body of cellular plastic with the skin by contacting a mass of a reactant isocyanatecontaining resin mixture with the skin while said unsaturated polyester remains in the liquid state, and then allowing said reactant mixture to react to form the cellular body, to copolymerize with said unsaturated polyester in the interfacial region between the skin and said body and to cure the polyester in the skin.

ELI SIMON. FRANK W. THOMAS. EDWARD H. BURKART.

References Cited in the le of this patent UNITED STATES PATENTS Number Number Name Date Malm Feb. 26, 1924 Freedlander May 5, 1925 Hood et a1 Dec. 14, 1926 Lower Oct. 11, 1927 Raovich June 24, 1941 Foote Apr. 20, 1943 Weaver Sept. 19, 1944 Urnston Feb. 5, 1946 Niessen Feb. 5, 1946 Norton Apr. 16, 1946 Pratt Nov. 11, 1947 Swedlow Dec. 14, 1948 FOREIGN PATENTS Country Date Great Britain May 22. 1932 

1. THE METHOD OF MAKING A LAMINATED ARTICLE COMPRISING PROVIDING LAMINATING MATERIAL CARRYING A WET POLYMERIZABLE UNSATURATED ORGANIC SUBSTANCE CONTAINING AT LEAST TWO GROUPS PER MOLECULE AS THE REACTIVE CONSTITUENTS, SAID GROUPS BEING SELECTED FROM THE CLASS CONSISTING OF VINYL GROUPS AND ALLYL GROUPS, AND SUBSTANCE BEING CAPABLE OF COPOLYMERIZING WITH ISOCYANATE MOLECULES, AND THEN BONDING A CELLULAR PLASTIC LAYER 